1. Field of the Invention
This invention relates to a distance measuring apparatus of the active type for use in an auto focus camera or the like.
2. Description of the Related Art
A distance measuring apparatus of the active type, as shown in FIG. 7 of the accompanying drawings, usually has a light projection lens 2 and a light receiving lens 3 fixed to a camera body 1, and light projected from a light projection element 4 through the light projection lens 2 is reflected by an object and is imaged on a light receiving element 5 through the light receiving lens 3. The imaged position on the light receiving element 5 changes in conformity with the distance of the object and therefore, the apparatus is designed such that the light receiving position is detected by a semiconductor position detector (hereinafter referred to as the PSD) and the distance to the object is calculated.
In the above-described example of the prior art, however, where a glass 6 is in front of the camera body 1, most of the light projected from the light projection element 4 through the light projection lens 2 is transmitted through the glass 6, but light which is slightly diffused and reflected between the front surface (or the back surface) of the glass 6 and the camera body 1 generally irradiates the light receiving element (PSD) 5 through the light receiving lens 3. Accordingly, when an attempt is made to photograph a distant view from an observation room in a multistory building or a tower through window glass, since the object is a distant view, principal rays transmitted through the glass 6 are not reflected back, while diffused and reflected light from the glass generally irradiates the light receiving element 5 and therefore, for example, a medium distance of 1 m to 2 m is measured, and this has led to the disadvantage that an out-of-focus photograph results.
This problem becomes particularly remarkable due to the shortened distance between the light projection lens and the light receiving lens resulting from the downsizing of the camera and has therefore formed a bottleneck in the downsizing of the camera.
Also, some of distance measuring apparatuses of the active type are provided with a plurality of distance measuring fields of view.
In a distance measuring apparatus having a plurality of distance measuring fields of view, as shown in FIG. 17 of the accompanying drawings, light projected from a plurality of light projection elements 1, 2 and 3 is projected onto objects 5, 6 and 7 through a light projection lens 4. The light reflected by the objects 5, 6 and 7 is imaged on a plurality of two-division SPCs 9, 10 and 11 through a light receiving lens 8. The reference numeral 12 designates a camera body including the distance measuring apparatus. The two-division SPCs 9, 10 and 11, as shown in FIG. 18A of the accompanying drawings, are comprised of SPCs 9F, 10F, 11F close to the light projection elements and SPCs 9N, 10N, 11F on the opposite side. The projected lights on the two-division SPCs when the object distances are 6 m, 1.2 m and 0.6 m are imaged as shown by 9B, 10B, 11B in FIG. 18B, 9C, 10C, 11C in FIG. 18C and 9D, 10D, 11D in FIG. 18D, respectively. The distances of the objects 5, 6 and 7 are found by calculating the ratio of a quantity of light on 9F and 9N, the ratio of a quantity of light on 10F and 10N and the ratio of a quantity of light on 11F and 11N.
In the above-described example of the prior art, however, when an attempt is made to photograph a distant view through the window glass of an observation room in a multistory building or a tower or through a train window, as shown in FIG. 19 of the accompanying drawings, most of light projected from the light projection element 2 through the light projection lens 4 is transmitted through glass 100, but light which is slightly diffused and reflected between the front surface (or the back surface) of the glass 100 and the camera body 12 generally irradiates the light receiving elements 9, 10 and 11 through the light receiving lens 8 and therefore, the result of the distance measurement from the output of the light receiving element 10 corresponding to the light projection element 2 is a medium distance of e.g. 1 m-2 m, and this has led to the disadvantage that an out-of-focus photograph results. 10 Also, if a medium distance is measured in any one of the plurality of fields of view, an out-of-focus photograph will result, and this has also posed a problem in effecting the enhanced specification of a camera, i.e., a plurality of distance measuring fields of view.